Thermostatic heater control



Sept. 16, 1952 w. A. MARSHALL, JR 2,610,796

THERMOSTATIC HEATER CONTROL Filed Sept. 28, 1945 4 Sheets-Sheet l Sept.16, 1952 w. A. MARSHALL, JR 7 2,610,796

' THERMOSTATIC HEATER CONTROL Filed Sept. 28, 1945 4 Sheets-Sheet 2 J05J26 K i #0 3. 104 Z T a E z 1/52 Sept. 16, 1952 w. A. MARSHALL, JR2,610,795

'THERMOSTATIC HEATER CONTROL.

Filed Sept. 28, 1945 4 Sheets-Sheet 3 i WM 6 9 arrleiS.

p 1952 w. A. MARSHALL, JR 2,610,796

THERMOSTATIC HEATER CONTROL Filed Sept. 28, 1945 4 Sheets-Sheet 4 2042oz Emmi- 29;

zzzz-m w/mmze Patented Sept. 16, 1952 THERMOSTATIC HEATER CONTROLWilliam. A. Marshall, J r., Chicago, Ill. assignon to Stewart-WarnerCorporation, Chicago, 111;,. a. corporation of. VirginiaApplicationscptembcr 28, 1945, Serial No. 613,118;

4 Claims. (01. 23.6--2.0)

1. This. invention relates to heating apparatus andzismore. particularlyconcerned, with, but not limited. to; heating equipment for. automobilesandsimiiarvehioles. 4'

In present automotive.- practice the passenger compartmentot a.vehicleis frequently heated by means. of ahot water radiator connectedto the engine cooling system. so. as to receive a supply of hot; waterfrom the water jacket of the internal. combustion. engine which drivesthe ve.- hicle. In. some installations, only a singleheater is used forthe entire passenger compartment, while. in. other installations two. ormore heaters are employed for-this. purpose. In. some arrangements thehot-waterradiator is mounted on the dash board: which separates theengine com.- partment from the passenger compartment; in other cases.the. heating radiator is located beneath the; front. seat of. a;passenger automobile. Various other arrangements of hot water heatersare provided; for. passenger automobiles; and. in buses several; heatersmay be located; at different. points in the. passenger space to: insurea. substantially uniform distribution. of the heating. effect.

With any of these arrangements. the heat radiating. unit. or units are.inefiective until the temperature of. the. water in the jacket. of theenginelhasbeen; raised. by operation of the engine itself- When. thevehicle has. been standingin the open or in an unheatedgarageior anappreciable length. of time incold weather, the water in the engine.coolin system is at alow temperature and some. little timeis required tobring the \vater'to asufiiciently high temperature to enable the heatradiating unitsto function. Most auto.- mobile cooling systems. includethermostatic. con. trols whichv prevent the. cooling water. or most. ofit from circulatmgzthrough the automobile. cooling radiator. untilithe.temperature .of the water in the water jacket. has reached apredetermined minimum value. The thermostatic control shortens the time.required to. bring the engine itself to normal-operating condition andalso the time required to raise the waterin the circulatory system toasufliciently high temperature so. that theheat radiating units; willbegin to: give oil? heat to the. passenger compartment. However, evenwith: the best. present installationsa. very appreciable. period of:time. is required. before. the heat units commence supplying'heat. ifthe. automobile and. its cooling system are thoroughly chilled: at.thestime the. is started.

One object of. thiscinvention. is to. provide. an auxiliary heatingapparatus for use; with. a; circalatory system having one or more heatradiating units and. which will materially shorten the time required.to. bring the water in. the system. to a sufficiently high temperatureto enable the radiating unitsto give of]? heat.

Another object of the invention is. to. provide an. auxiliary heating,apparatus which can be installed in the circulatory systems of existingautomobiles and which. is adaptedto :loe usedwith any type of hot waterheating; unit.

A further object of the invention is to. provide new and improvedpreheating apparatus for use in connection with the liquid coolingsystem of an internal combustion engine and which is adapted to raisethetcmperature of the liquid in the system independently of. the heatradiated by the. operation. of the engine so as to facilitate startingthe engine and to improve the. efiiciency of its operation immediatelyafter starting.

It is also an object. of the invention to provide new and improvedheating apparatus applicable to the circulatory system oian internalcombustion engine, particularly when such a system includesv a heatradiating, unit or units, and having automatic controlling meansservingtostart and stop the. operation. of the auxiliary heater inaocordance with temperature requirements, of the system.

More. specifically, it. is an objector. the invention to provide. newand. improved heating apparatus having a burner, a combustion chamber,and a water jacket with connections by which said jacket. may :beincluded in the circulatory cooling system of an: internal combustionengine, together with thermostatic means. controllingthe operation ofthe burner and located closely'adjacent thewater outlet. of the jacketso as to. be responsive to the. temperature. of thewater as'it comesfrom the heater for delivery to. the heat radiating; units of thevehicle. the heater being coupled between the; water jacket of the.engine and the; radiating units. in the. vehicle compartment so that ifthe temperature; of the Water flowing through the heater. from the.engine is high. enoughthe heater-itself will not he. required tooperateto furnish heat to the compartment.

It is also an object. ofv theinvention to provide a newand improvedinternal combustion heater having a Water jacket with connectionstherefrom to, a circulatory system, the heater including an electricallyoperated. igniter, an electrically driven. blower for providingcombustion; air, and an electrically controlled. fuel. feedin valve, andhaving. a singlethermostatic means arranged to control; these electricaldevices in a definite stage.

An additional object of the invention is to provide switch mechanismresponsive to the temperature of the water and operative in sequence tode-energize the igniter, then to reduce the rate of fuel supply, andfinally, at a predetermined maximum temperature, to shut off the fuelsupply and stop combustion in the heater, but with V the switchmechanism so arranged that the feeding of fuel to the burner cannot beresumed unless the igniter is also energized.

Other objects and advantages will appear from the following description,taken in conjunction with the accompanying drawings.

In the drawings: a 3

Fig. 1 is a vertical sectional view showing a heater and control devicesapplied thereto embodying this invention; 1 e

Fig. 2 is a detail section taken as indicated at line 22 onFig.1;' I aFig. 3 is a vertical axial section of the electrically operated fuelcontrol valve for the heater together with the igniting device; 7

'Fig. 4 is a detail plan section taken as indicated at line 44 on Fig. 3and on a smaller scale;

Fig. 5 is a detail section taken as indicated at line 5-5 on Fig. 3;

Fig. 6 is a vertical sectional view on an enlarged scale showing thecontrolswitches and their actuating bellows;

Fig. 7 is a plan view of the switches taken as indicated at line T-l onFig. 6; v

Fig. 8 is an end elevation of the same taken as indicated at line 8-8 onFig. 6;

Fig. 9 is a wiring diagram for th switch device illustrated in Fig. 8;

Fig. 10 is a vertical sectional view similar to Fig. 6, showing a'modified form'of switch device for I thesame purpo'se;'

Fig. 11 is a wiring'device for the switch device shown in Fig. 10. Y

As shown in Figs. 1 and 2, the heater which is designated generally bythe numeral [0 is of cylindrical form and includes a cylindricalcombustion chamber I2 having an end wall 14 and having an initialcombustion space or burner defined by a wall It of truncated conicalform extending from the wall I4 into-the end or the cyf lindricalchamber [21 The liquid fuel for the combustible mixture 'is suppliedthrough a, restricted orifice [8 leading 'from the fuel control valvedevice denoted by' the numeral 20; the liquid fuel is discharged into apocket 22'containing an electrically energized igniter 24 of theincandescenttype and openinginto the burner space within the conicalwall It. 'Airfor the combustible mixture is supplied by a rotary blower2B driven by a motor 28 and discharging the air into a feed pipe 39'which terminates in a portion 32 extending through the conical wall [6in a direction substantially tangential thereto. The air entering theburner space within the wall [6 is thus given a whirling motionasindicated by the arrows in Fig. 1 which facilitates thoroughintermixture of the airwith'the liquid fuel. The mixture is ignitedinitially by'heat from the incandescent element 24 and the flameproceeds through the combustion chamber l2 from the burner space towardthe opposite end of the chamber. The cylindrical wall 34 of the chamber12 terminates in spaced relation to the end wall 36 so that thecombustion space l2 commum'oates with an annular space 38 surrounding itand leading to the annular channel 451 and the exhaust passage 42extending therefrom.

The water jacket for the water which is to be heated by the products ofcombustion is in two parts; the inner jacket 44 is defined by thecylindrical wall 34 of the combustion chambe and a cylindrical wall 45spaced from it as seen in Fig. l. The outer jacket 48 is containedbetween the outer cylindrical wall 50 of the heater and an innercylindrical wall 52 spaced therefrom and from the wall 46. Thecombustion space Ed is thus disposed between the walls 46 and 52 so thatproducts of combustion are in heat exchange relation with both walls ofthe jacket 44 and with the inner wall 52 of the jacket 48. An inlet pipe54 extends from the circulatory system of the vehicle engine intoconnection with the outer jacket 48 as seen in Fig. 2, and in alignmentwith this inlet pipe 54 there is provided a connecting thimble 5Bafiording communication with the in ner jacket 44 so that the in-fiowingwater divides between the two jackets and passes upwardly around bothsides of the combustion chamber H2. The water outlet 58 is shownextending from the upper side of the heater casing 50 and incommunication with the outer jacket 48. A thimble 6G is arranged inalignment with the outlet 58 for interconnecting the inner jacket 44 andthe outer jacket 48 and providing a direct outlet from the inner jacket.The outer jacket 48 includes a space 62 at the end of the combustionchamber 12 between the end wall 36 thereof and the end wall 54 of theheater.

The liquid fuel for the heater is preferably supplied by an enginedriven pump (not shown) and flows from a feed pipe 10 into the fuel bowlI? of the control valve device 20. This valve device is shown in detailin Fig. 3 and includes an inlet valve 74 carried upon a supporting body15 of triangular cross section having a spring 76 pocketed therein andarranged to uphold the'valve body 15 and the valve 14. This valveco-operates with a valve seat 13 formed in the fitting 89, The fittingis screwed into the inlet passage 82 with which the feed pipe 16 isconnected and is formed with an outlet port 84 through which the liquidfuel is delivered to the fuel bowl 72 when the valve 14 is opened. Fuelunder pressure flowing through'the valve port 84 and into the bowl l2builds up a pressure therein because of the outlet restriction l8'untilthe upwardly acting force of the bowl pressure against thediaphragm 83 balances the. variable force of an electromagnetic means tobe described presently and as is more fully described in a co -pendingapplication, Serial No. 577,239, filed February 10, 1945, nowabancloned, and assigned to the'assignee of this application.

The fuel bowl or chamber 12 is formed with a flange 86, and a flexiblediaphragm 88 clamped against it by a ring 98 serves as an upper wall forthe fuel chamber, as seen in Fig. 3. An elec-- tromagnet surmounting thering 90 includes a coil 92 fitted onto a core $4 of magnetic materialsecured at its lower end in a plate 96 which is also. of magneticmaterial. Clamping screws 98 extend through the marginal portions of theplate '96 and through'the ring 90 and fiange' 86 for securing thediaphragm 88 in position and toot flange I02 is; secured by the screws98; thus the upper end of thewcore. 94 forms one pole. of magnet. whilethe annular upper end of the cylinder HIO forms the opposite. pole, withan air: gap; at. I04. An armature I06 in the form of an inverted. cupvis arranged with its flange I08 in the airgap I04 and a brass stem I I0to which the armature. is adjustably threaded extends freely through anaxial bore in the core 94. The

lower end 01' the stem .0 engages a contact button II2 clamped in thecenter of the diaphragm 8'0, with its head engaging the lower face ofthe diaphragm and having a cupped washer I I4 fixed on the shank of thebutton and engaging the upper face of the diaphragm. A short rod orstem' I I0 extends through the port 84- in the upper end 01 the fitting80 and when the coil 92 is energized and the armature I06 and its stemIIO are. drawn downwardly by magnetic attraction, this movement "is.transmitted through the button H2 and rod I16 to the valve I4 to unseatthe latter and permitfiow oi liquid fuel from the feed pipe I0 throughthe bowl I2 and through its outlet passage H8 which Ieads'to therestricted orifice I8 through which the fuel is discharged to theburner. The rate at which the fuel feeds through the orifice I8 dependsupon the pressure required in the bowl 12 to balance the magnetic forceof the coil 92, and this in turn varies with the strength of currentsupplied to the coil 92. Armature- I 06 is centered in the annular airgap I04 by a three-armed spider I preferably of spring brass carried bya hub I22 threaded to engage the threaded upper'end of the stem H0.

The arms of the spider I 20 are attached by bolts I to the flange I28 ofa brass or aluminum sleeve I28 telescopically secured to cylinder I00. Aflange casing I32 encloses the'magnet assembly and is fastened to thering 90 by screws I34.

The water from the cooling system of the engine (not shown) enters theheater jackets through the inlet pipe 54' and leaves by way of theoutlet elbow- 58 which ends in a reduced portion I36 to which a hose I38is secured. In the portion I40 of the-outlet passage there is mounted aheat responsive Sylphon bellows I 42 controlling a valve I44 whichregulates the rate of how of water through the entire circulatorysystem.

When the water is cold the valve I44 will be closed, but as thetemperature of the water rises,

the valve willbemore or less opened by the vapor pressure of the liquidsealed in the Sylphon I42 and more rapid circulation through the systemwill be maintained, usually by; an engine-driven pump associatedtherewith. V

The operation of! the heater is controlled automatically in response totemperature of the water at the outlet 58. A temperature responsivebellows I46 is mountedon a bracket I48 and the interlor of the bellowsI46 is in communication withthe bore of a tube I50 extending into. theoutlet elbow 58. As shown, the tube I50 terminates within a bulb I52which contains the liquid, the vaporization ofwhichoperates the bellowsI46. The threaded head I54; of the bulb is secured in the wall of theoutlet 58 with the bulb I52 projecting in the path of; the out-flowingwater.

The bracket I48 also supports three electrical switches for control ofthe heater. As shown in Fig. 6, the upper endof the bellows I46 includesa recessed head or end wall I56 in which the headedlower end I58 of anactuating rod I60 is secured so that the rod will moveup or. down inresponse to expansion or contraction of the bellows 140.. The upperswitch includes a. movable-arm IE2 and. a. fixed. contact I64.Immediately-below thisis. another switch having a movable: arm I86 and;a. fixed arm. I68. The third switch is shown with a movable arm I10 andfixed contact [12. The. rod, I 60 passes through clearance aperturesineach of the movable switch. arms andis provided. with shoulders whichare spaced along the rod. I60 for actuating the movable. arms in a.predetermined sequence. As the. temperature rises and causes. expansionof the bellows I46, the uppermost. shoulder I14 oi the rod IEO. engages:the switch arm. I 62. and separates it from the fixed contact I 64. Witha further increase of: temperature and expansion of the bellows I45 theshoulder I16 engages. the switch arm I10 and. separates: it from. itsfixed contact I12. The. flexibility of the arms I62. and I10 permitsthem to be carried upwardly still further aftertheir' initial separationfrom the fixed contacts. so that. with. additional expansion of thebellows I46 the. shoulder I18 on. the. sleeve I which is slidabl'e. onrod I80. will engage the switch arm I68 and separate it from the contactI68.

As a convenient construction. Fig. 6 shows the fixed contact "arms. I64,I68 and I12 supported by a pair of upstanding bolts I82, each sheathedin a tube of insulating material I84 over which blocks I88 also ofinsulating materialv are assembled in positions to space apart the.apertured' end portions ot'conta'ct arms I64, I68 and I12. Insulatingplates I88. are disposed above and below the assembly of contacts with ametallic washer'plate I90 under the heads of the belts I82. A connectorvlug I92 is fitted over the bolts I82 in face contact with each of the.members I64, I50 and I12, and said lugs have terminal portions I94 whichextend laterally as shown in Fig. 7' forconnection with terminal leadwires. The bolts I82 pass through openings in the shelf or base I98which is secured to the bracket arm I48 and are clamped in position bynuts I88.

The movable arms I62, I66 and. H0 of the switches are supported in asubstantially similar manner; and in Fig. '6 the corresponding'parts ofthe assembly are designated by the same numetals as the parts whichsupport: the fixed contacts as just described.

Fig. 9 presents a wiring diagram in which the switch of Figs. 1 and 6 isemployed. A source. of electrical energy is indicated as a battery 20!]having one terminal grounded at 202 and having the other terminalconnected toa main switch 204 through a conductor 206 leading to a relaycoil 2-08 and thence through a conductor 2I0 to the movable switch: armI62. It may be understood that when the heater is cold all three switcharms I62, I66 and I ID will engage their corresponding fixed contacts;accordingly, the closing of the main switch 204 will establish a circuitthrough coil 208 since the fixed contact I64 is grounded. The relaycoil, upon being energized, actuates two movable switch arms; the

" arm 22 is engaged with contact 2I4 so that a circuit is establishedthrough conductors 208 and 216' through switch arm 2I2 and conductor 2IBthrough the igniter coil 24' previously described. The igniter' isgrounded at 220 as shown in the diagram. The other switch arm 222,actuated by the relay coil 208, engages contact 224 and establishes acircuit through conductor 226 to the movable switch arm I'I0, thencethrough the fixed contact I12 and conductor 228 through the coil- 02 ofthe magnetic fuel control valve shown the switch arm in Fig. 3. Asindicated in said Fig. 3, one terminal wire 93 of the coil 92 isgrounded'on the metallic shell I; the other lead wire extendsto athreaded terminal 95 outside the enclosing cover I32 for connection withthe lead wire 228.

To complete the requirements for proper operation of the burner, theclosing of the contacts 222-224 also provides current for operating themotor 28 of the combustion air blower 2'5 which has one terminalconnected to the conductor 22% while the other terminal is grounded at23c. Thus when the main switch 204 is closed and the bellows I46 isstillcold enough to leave all of the three switch arms I62, I66 and I'll? inclosed position, the igniter 24 will be energized and renderedincandescent, the magnetic fuel valve 72 will be opened, and thecombustion air blower 25 wi l be started so that a combustible mixturewill be supplied and ignited in the burner space with the wall It andthereupon combustion will proceed through the chamber I2 and itsconnected passages leading to the exhaust 42.

As soon as this has continued long enough to raise the temperature ofthe water to a'predetermined minimum value, say, for example, 145 F.,the bellows I48 will expand sufficiently to engage the shoulder I74 ofthe actuating rod I69 with the switch arm I52 and to lift said'arm outof engagement with the contact I 8 3. This will open the igniter circuitbyde-energizing the relay 208 and allowing the movable switch arm 2I2 todisengage the contact 2M, Combustion will proceed without the assistanceof the electrical igniter 24, but thede-energizing of the coil 298 opensthe switch 222 as well as the switch 2I2 and breaks the original circuitleading to the combustion air motor 28 and also the circuit for themagnetic fuel valve. Therefore, a hold ing relay is provided for thesecircuits having a coil 232 which is connected, to the conductor 225 andthe other end of the coil is grounded through the switch arm I66 and itsfixed contact :58. When the coil 232 isenergized, the relay switchmember 234 connects the blower motor 28 to a conductor 236,1eadingdirectly from conductor 26% to supplycurrent from thebattery 266. Therelay switch 234 and conductor 23% also provide a substitute circuit forsupplying current to the coil 92 of the magnetic fuel control valve byway of the switch IIil, ii 2 and coni,

switch arm I10 and lifts it out of engagement with its contact I72. Thisforces the current to how from conductor 225 to conductor 228 through aresistance 238, thus furnishing lesscurrent-to the coil 92 of themagnetic fuel control valve and permitting the fuel pressure partiallyto close the valve I4. This reduces the rate of fuel fed to the burnerand may prevent a further rise in the temperature of the water. However,if the temperature continues to increase, the bellows I46 will lift theshoulder I18 into contact with I55 and then disengage said arm from itsfixed contact I68, thereby opening the circuit of the holding coil 232.This opens the relay switch 234, stopping the motor 23 for thecombustion air blower and also depriving the coil 92 of current forholding the fuel valve M open. Accordingly, the'operation of the burneris arrested'and it'willnot be resumed until the temperature of the waterat 58 hasdropped to' the predetermined value at which the switch arm I52is lowered into engagement with the contact I64 by contraction of thebellows I25. Before this occurs the arms I66 and I10 will have beenreturned to their initial positions engaging contacts I63 and I12respectively so that the original condition of the circuits will berestored. Assuming that the main switch 2lldshas been left closed, thecycle just described will be repeated and this will occur atsufilciently frequent intervals to prevent the temperature of the waterleaving the heater at the outlet 58 from falling below 145 F. orwhatever predetermined value has been fixed as a minimum. On the otherhand, if the heat supplied to the water in the system by operation ofthe internal combustion engine is sufficient to maintain a watertemperature in excess Of 145 F., then the bellows I46 will remaindistended sufiiciently to hold the switch arm IE2 at open position, thuspreventing operation of the heater and relying upon the engine to supplysuflicient surplus heat for warming the passenger compartment of thevehicle.

As an'alternative arrangement, to avoid the use of relays Figs. 10 and11 show a switch mechanism to be actuated by the thermostatic-bellows546, Fig. 11 indicating the circuits controlled by the switch device.The switch mechanism comprises three fixed contacts 250, 262 and 21K]carried by substantially rigid arms which extend from an insulatedsupport secured to the shelf portion 591 of the bracket structure whichalso carries the Sylphon bellows I46. The support includes upstandingbolts I23 enclosed in insu lating sleeves I and provided with spacingblocks E81 and spacers I89 between which the parts of the switches areclamped. The fixed contact arms 259,. 260 and 210 are supported orreinforced by arms of insulating material 25L 2N and 27 I. Th fixedcontact 256 normally engages a movable contactarm 252having one endclampedibetween the insulating spacers I85 along with one end of itsactuating blade 253. The outer end of the contact arm 252 is engagedwith the actuating blade 253 bymeans of a U shaped spring member 254which operates in the manner of a toggle to swing thearm 252- downwardlyand separate the contacts when the blade 253 is moved upwardly. g w

The fixed contact 2% cooperateswith a mov able arm 262 having anactuating b1ade.26 3 and a U -spring 26 3, these parts beingsimilartothose of the switch just described and-operating in the same manner.The uppermost switch which includes the hired contact 2lll is shown witha movable contact arm 272, an actuating blade-213 therefor and aU-spring 2M connecting the arm in the blade. All three switches operatewith a snap action in separating their contacts; that is, theactuatingarm of the switch moves for some distance before causing anymovement of the movable contact arm but building up a stress in the U-spring so that when theactuating arm reaches a given point in itsmovement the switch arm is suddenly snapped in the opposite direction bythe stress of the spring. In the case of the two lower switches theactuating arms 253 and 263 when moved upwardly are merely sprung awayfrom their normal straight positions and will tend to return when theupward pressure is relieved. .As they return, their movable contact arms252 and 262 will be snapped backinto con tact position. The uppermostswitch shown in Fig. 10 difiers slightly in that the actuating arm 213wll remain at'either limitof its rangeand 1 1 has cooled somewhat belowthe point at which the heater was shut off (165 F), the circulation willbe maintainedbetween the engine jacket and the heater jacket ad the heatradiating units in the passenger compartment of the vehicle making useof any heat which iscontributed by the engine itself. As alreadyexplained, after the heater has been shut off at 165 F. it will notbegin operating again until the water temperaturehas dropped to thepoint at which the igniter switch was opened and at which the igniterwill be reenergized, namely about 145 F. The lowest critical temperaturein the system thus is 145.F. and the heater will not be called upon tooperate until the water temperature drops to this point. Ordinarily, andexcept in extremely cold weather, the operation of the engine willmaintain the water, at a satisfactory temperature for heating thepassenger compartment without assistance of the internal combustionheater of this invention. However, after the. engine has been stoppedand the water in the system has become quite cold, the operation, oftheheater will greatly facilitate warming up of the engine while at thesame time producing a comfortable temperature in the passengercompartment. without undue delay. i

Preferably the operation of the bellows H36 and the switches connectedthereto is effected by a quantity of fluid having a low boiling point,

such as ethyl alcohol, which isliquid atordinary temperatures andoccupies only a portion of the space in the bulb. I52, tube- I50 andbellows 14%..

Upon increase of temperature the vaporization of this liquid exerts avapor'pressure which operates the bellows I46. One advantage of thisarrangement is that the system is not critical as to volume since at'acertain temperature, depending upon the particular fluid employed, aportion of the fluid willboil and fill the system at a predeterminedpressure, rendering it operative thereafter to actuate the switches inthe manner already described.

It also is preferable that this system including the bellows I46 andthe-bulb I 52 be initially evacuated below atmospheric pressure, causingthe bellows to assume a contracted position. As the bulb heats up thevapor pressure ofthe fluid therein approaches atmospheric pressure, thuspermitting the bellows to expand and operate the switches. With thisarrangement, however, if the bellows should crack or the'system shouldotherwise develop a leak, atmospheric air will leak into the system,raising the pressure therein and permitting the bellows to expand andcausing all the switch contacts to be opened. This is inthe interest ofsafety since the failure of the control system results merely inshutting off the heater rather than permitting it to operate withoutproper control.

While there is shown and described herein cer-' tain structure embodyingthis invention, it is to be understood that the invention is not limitedthereto or thereby but may assume numerous other forms and that itincludes all modifications, variations and equivalents coming within thescope of the claims.

I claim:

1. In an internal combustion heater which includes an electricallyenergized igniting device, a fuel inlet valve for said heater, anelectromagnetic control device for said valve, a source of 12 electricalenergy and circuits in-which said source s connected wi h sa d e i es, afi t sw tch operative when closed to energize -the igniter, a secondswitch operative when clos d. to hold thev fuel 'valye, at fullyopenposition, a-third switch operative when closed to hold said valve atpartially open position, said valve'closing'upon the opening of saidsecond and third; switches, and a single heat responsive devicesubjectto the heat output of the heater and including a movable member whichopens the first switch at. a prede-J termined temperature and opens thesecond switch at a-predetermined higher temperature, finally opening thethird switch at a predetermined maximum temperature to shut off the fuelsupply and interrupt the operation of theheater.

2. In a heater as defined in claim. 1, means which prevents re-openingof the fuelvalve until the igniter switch is closed.

3. Ina heatera definedin claim Lsaid third switch being. constructed toremain open until positively closed and said movable member ineludingvmeans for positively closing said third switch after said member haseifected the closing of the first and second switches in its returnmovement in response to cooling of the heat responsive device.

4. In an internal combustion heater, the combination of an electricallyenergized igniting device, electrically energized means. for controllingthe supply of fuel to the heater, a source of electrical energy, heatresponsive means subject to the heat output of the heater, switchingmeans operable by the heat responsive means selectively to energize theigniting device and the fuel controlling means from the source, theswitching means including means to terminate energization of theigniting device at a predetermined temperature, means to operate thefuel controlling means to terminate fuel fiow at a predetermined highertemperature, and means'to prevent operation of the fuel controllingmeans to commence fuel fiow until the igniting device is energized,after said fuel controlling means has terminated fuel flow at saidpredetermined higher temperature.

WILLIAM A. MARSHALL, REFERENCES CITED UNITED STATES AT N'rs Number DateName 1,220,985 Harter Mar. 27, 1917 1,316,021 Doble Sept. 16, 19191,395,399 I Doble et al. Nov. 1, 1921 1,529,906 Morris Mar. 17, 19251,918,265 Hartwig July 18, 1933 1,923,614 Clarkson Aug. 22, 19332,012,067 Mayo Aug; 20, 1935 2,044,427 Giesler June 16, 1936 2,046,643.Mackintosh July 7, 1936 2,046,812. 'Danuseret al. -July 7, 19362,162,571 Bock June 13, 1939 2,249,844 Martin July 22, 1941 2,257,755Morici et al Oct. 7, 1941 2,257,756 Morici et al Oct. 7, 1941 2,300,011Rose Oct. 27, 1942 2,303,382 Newhouse Dec. 1, 1942 2,429,101 Leslie 1Oct. 14, 1947 2,463,908

Rose Mar. 8, 1949

